The wide spread popularity in recent years of pick-up trucks and sport utility vehicles for both on-road and off-road use in business, recreational as well as everyday travel has popularized the "rugged" styling of such vehicles, as well as their accessories, from both the practical as well as aesthetic standpoint. Thus the exterior running board construction provided for such vehicles, both as original equipment and after-market accessory type products, has seen the advent of a simple large tubular support, typically in the form of a two or three inch diameter steel pipe bent-formed at its opposite axial ends for connection to the undercarriage of the vehicle. A straight run central portion of the pipe is typically positioned outboard of and below the door sill of the cab of the pick-up truck or the front and/or rear doors of a sport utility vehicle (SUV). Such pipe running boards provide both the rugged strength and structural support required for such use, and are also resistant to damage from traveling through underbrush as well as from various other types of misuse encountered in the typical service life of such vehicles. Also, since the pipe is spaced outboard of the vehicle body metal it is easy to clean off, as by a hose-down, mud clinging to the surface of the pipe and to the step carried by the pipe.
Although the use of a simple pipe in and of itself has been proposed and marketed with some success, safety considerations require that a step plate of some type be mounted on top of the pipe and provided with a ribbed, corrugated or other contoured gripping pattern on its upper face. This insures safe and secure footing by users of the running board both during entry and departure from the vehicle passenger space, as well as when riding in a standing position on the running board. Hitherto, such a pipe and step plate running board construction has been provided by mounting a step plate, made as a plastic extrusion, onto the opposed edges of an upper cut-off section of a metal support pipe. The step plate was supported along its longitudinal center line by support a support beam in the form of a piece of untreated pine wood board inserted into the metal pipe. The board rested along its bottom longitudinal edge on the bottom interior of the pipe and was dimensioned so that its upper longitudinal edge abutted the underside of the plastic extrusion step plate. However, this arrangement tended to become loose and disassembled from use and abuse under normal wear and tear conditions, as well as from swelling of the wood support from water collecting in the pipe. Thus, this prior commercial construction did not provide a fully secure mounting of the step plate on the pipe and hence could be pried off during running through heavy brush or similar extreme but not unusual conditions encountered during the off-road use of such vehicles. Accordingly, it has been previously proposed (but not produced or reduced to practice) to provide a step plate/pipe running board construction in which the wood interior brace is replaced by an injection molded plastic member spanning the length and width of the interior of the pipe beneath the slotted portion of the pipe to serve as an insert support structure for a separately manufactured step plate to be mounted thereon. However, this proposed design presented problems as to its mounting assembly into a straight pipe section in order to capture the support member within the pipe, and involved an expensive and impractical procedure for assembly. Hence, this design was abandoned as being not satisfactory at least from the standpoint of secure mounting, ruggedness and/or economy of manufacture and assembly.